Hello Dear, I am a Brazilian, so let me try to answer your question the best possible way.
We do hook ups and we do have night stands. Now, As a woman we do not have a night stand if we are really interested in the guy. The mentality of the Brazilian men usually a girl that sleeps with the guy in the first night it is not for a serious relationship. Man do not see very well a night stand girl. Of course every rule has an exception, but that is what they think, and if you have a night stand and they call you later is only for sex, nothing else.
Is it very common? Some do it, some don't. The majority of the guys, I would say about 95% do not respect a girl that has night stand. Of course they will take advantage of, but the girl is considered a flat out whore.
The majority of the population is Catholic and we are raised in the way that we must save ourselves.
Yes we are in a more modern society, but off course some customs still prevail.
Girls more from a big city, such as Sao Paulo and Rio would have a night stand. Outside those areas not too often.
What is the importance? It is really not important. Night stand it is only sex, and that is all. Again, the way we think, we like the guy we do not sleep with him, we make him wait because he will respect us and he will want to have a serious relationship. Girl that has a night stand it is not serious, that is how we think.
Now if he is really interested in you and you are interested, go ahead. Brazilian guys, if they are not interested they run away. Really. They are too coward to say that they are not interested on you, so they disapear.